Allergies and Allergy Testing
Allergies are among the most common problems patients experience. The manifestation of allergies varies. Some patients have recurrent sinus congestion and “infections.” Others have eczema, G-I distress, headaches, and various other symptoms. The ambiguous nature of these symptoms frequently makes the correlation between allergies and physical symptoms difficult to recognize.
Fortunately, there are increasingly useful ways to diagnose and treat this problem. Most people with episodic allergy symptoms can use oral medications such as antihistamines. Benadryl is arguably still the most effective antihistamine, but the associated sedation can be problematic. Newer non-sedating antihistamines (Zyrtec, Claritin) can be employed, but they are typically more expensive. Inhaled nasal steroids (Flonase, Nasarel, Nasonex, etc) are very useful, but they take several days to begin working, and they must be used daily for sustained relief. Singulair represents a very promising newer class of medication called leukotriene blockers.
If the symptoms are mild and intermittent, then the measures described above are often adequate. However, when the problems are persistent and more severe, then it is more desirable to identify the offending allergen and avoid it if possible. If, as is so often the case, the allergen cannot be avoided, then desensitization may be helpful(perhaps 80%-90% of typical allergy problems can be treated this way).
Common offenders include dust, mold, mildew, foods, pet dander, pollens, and other everyday contacts. In order to find which allergens are causing problems for a particular person, then we need to take a a thorough history of potential allergen exposure, and then run tests to see how their system reacts to various compounds. The easiest way to do this is to send blood to the lab. If one is allergic to a particular compound, then antibodies are formed again this antigen (allergen). When the lab exposes the blood from the patient to various antigens (allergens), then any antibodies present in the blood should cause a reaction to corresponding antigens and allow the lab to determine which allergens are causing problems in that patient. This method of testing is called RAST testing. Unfortunately, RAST testing has the limitation of occurring outside of the body in an artificial lab setting. It does not necessarily indicate how a patient might respond to that allergen in the clinical setting.
A more accurate way to test the patient is through scratch testing or patch testing. This method involves applying allergens directly to the skin and assessing the response. This is much more specific and useful in deciding how to approach desensitization therapy. The main disadvantage is that it may take several days to complete this test, and it is substantially more expensive. Unfortunately, insurance does not always cover allergy testing. The expense of testing and subsequent desensitization can represent significant barriers.
Desensitization involves identifying the allergen, then exposing the patient beginning with such small amounts of the allergen that the immune system "sees" the allergen but does not feel it need to respond. The dose is gradually increased until it reaches “real-world” levels. If the tests are accurate and the vaccines are properly mixed, then this usually results in “hypnotizing” the immune system into a state of tolerance for those specific allergens. However, one must continue using the desensitization shots regularly to keep the immune system “hypnotized.” Otherwise, it “wakes up” and reacts as it did originally.
Thomas L. Horton, MD